This invention relates generally to a medical imaging phantom, and more particularly to a cardiac phantom for use in medical imaging for diagnostic purposes.
A number of different nuclear imaging instruments have been devised for diagnosing patient aliments and conditions. The field of use of such instruments is known as the field of nuclear medicine. Nuclear imaging instruments are advantageous in that they can produce images of conditions within soft tissue organs of a patient""s body without exploratory surgery.
In the practice of nuclear medicine, a low level of a tracer radioisotope is injected into a patient. The tracer radioisotope is carried in the patient""s bloodstream to the patient""s internal organs, such as the heart, liver, kidneys, or brain. The tracer radioisotope emits gamma rays, a portion of which pass from the patient""s body and are detectable by nuclear imaging instruments and reflect, for example, blood flow or metabolic function in the organ.
In order to calibrate and check the accuracy of nuclear imaging instruments, test structures, known in the field as phantoms, are utilized. Other prior nuclear imaging phantoms have been produced in forms which encase radioactive sources within a structure which simulate the shape and gamma ray attenuation properties of the human body. Such conventional test phantoms may employ concentrated radioactive sources which are imaged as xe2x80x9chotxe2x80x9d spots or small non-radioactive structures within a homogenous radioactive source which exhibit xe2x80x9ccoldxe2x80x9d spots in the image produced. The nuclear imaging instruments are used to produce images of the phantom. By examining the images produced, the degree to which the image conforms to the actual phantom structure and the degree to which irregularities exist in the image are ascertained.
Nuclear imaging is a common non-invasive technique used in the evaluation of cardiac function and disease. Left ventricular ejection fraction and volume measurements are central to the objective characterization of cardiac performance. They are widely used as prognostic and therapeutic indicators in patients with different cardiac diseases. The importance of the measurement of the left ventricular ejection fraction and volume has been well recognized. Thus, the accuracy of the ejection fraction measurement and volume estimation performed by nuclear imaging devices with dynamic cardiac phantoms is important.
Conventional cardiac phantoms of various sorts have been used extensively to study and validate measurements by nuclear and other medical imaging devices. Left ventricular models and casts have served as primary reference standards to validate imaging methods. However, cardiac phantoms are limited in applicability because they are static, or not anatomically realistic in shape. In particular, past cardiac phantoms have been particularly inadequate in simulating a beating heart. Moreover, substantial problems still complicate accurate measurements of left ventricular contractility. Realistic, expansible phantoms of the left ventricle to simulate the left ventricle of the beating heart are needed for use in left ventricular ejection fraction and volume measurement under various simulated clinical conditions.
For the foregoing reasons, there is a need for a new, more realistic cardiac phantom. Specifically, the new phantom should be a beating phantom which allows real time nuclear imaging. In particular, the new phantom should allow medical imaging and measurement of the left ventricular region during all phases of the heart action.
According to the present invention there is provided an apparatus for simulating a dynamic cardiac ventricle. The apparatus comprises two concentrically-disposed, fluid-tight, flexible membranes defining a closed space between the walls of the membranes. A pump is operatively connected to the inner membrane for reciprocally delivering a volume of fluid to the inner membrane to inflate and deflate both membranes in simulating systole and diastole of a heart. A medium is disposed within the closed space defined between the walls of the membranes for maintaining a uniform distance between the walls of the membranes during inflation and deflation.
Also according to the present invention, a phantom is provided for evaluation of a medical imaging system. The phantom comprises a closed container of fluid and a simulated dynamic cardiac ventricle disposed within the container. The simulated cardiac ventricle includes two concentrically-disposed, fluid-tight, flexible membranes defining a closed space between the walls of the membranes and a medium disposed within the closed space defined between the walls of the membranes for maintaining a uniform distance between the walls of the membranes during inflation and deflation. A fluid delivery system including a pump between the container of fluid and the inner membrane provides a reciprocating volume of fluid between the container and the inner membrane to inflate and deflate both membranes in simulating systole and diastole of a heart.
Further according to the present invention, a method is provided for controlling an apparatus capable of simulating a cardiac ventricle. The method comprises the steps of determining data points for a ventricular volume versus time curve, sampling a position of a pump motor, determining the pump motor position and at least one subsequent position of the pump motor corresponding to the volume versus time curve, calculating velocity and acceleration to reach the subsequent position to simulate a cardiac ventricle, and moving the pump motor to the subsequent position based on the calculated velocity and acceleration.
A computer system is also provided according to the present invention for controlling an apparatus capable of simulating a cardiac ventricle. The computer system comprises means for determining data points for a ventricular volume versus time curve, means for sampling a position of a pump motor, means for determining the pump motor position and at least one subsequent position of the pump motor corresponding to the volume versus time curve, means for calculating velocity and acceleration to reach the subsequent position to simulate a cardiac ventricle, and means for moving the pump motor to the subsequent position based on the calculated velocity and acceleration.
Still further according to the present invention, a computer-readable medium is provided. The contents of the medium cause a computer system to control an apparatus capable of simulating a cardiac ventricle by performing the steps of determining data points for a ventricular volume versus time curve, sampling a position of a pump motor, defining the pump motor position and at least one subsequent position of the pump motor corresponding to the volume versus time curve, calculating velocity and acceleration to reach the subsequent position to simulate a cardiac ventricle, and moving the pump motor to the subsequent position based on the calculated velocity and acceleration.